(a) Field of Invention
The present invention relates generally to check valves permitting flow of fluid media in one direction only and particularly for check valves used to control the flow of corrosive, chemically active, or sensitive fluids such that inert materials are required for all surfaces exposed to the fluid media.
(b) Description of Related art
A number of direct acting check valves exist which consist essentially of a disc traversing a flow passage such that back pressure forces the disk against a valve seat to block the reverse floW. A common limitation of such valves is that a high rate of sensitivity whereby the valve cracks and reseats at low pressure differentials is difficult to achieve in a valve that is also capable of functioning over a wide range of flow rates and pressure conditions. Generally, a high degree of sensitivity is achieved only by incorporating design features which limit the range of conditions under which performance is satisfactory. The particularly limited mechanical properties of suitably inert materials increases the difficulty of designing a valve that will not fail when exposed to high pressure in the blocked direction. A problem with inert materials is their tendency to take a compression set or stick when subjected to high pressures.
Existing U.S. Pats. which may be similar to or pertinent to this invention are as follows:
______________________________________ U.S. Pat. No. Inventor Date ______________________________________ 3,889,710 Brost 06-17-75 4,141,379 Manske 02-27-79 4,354,492 McPhee 10-19-82 4,415,003 Paradis, et al. 11-15-83 4,556,086 Raines 09-03-85 ______________________________________
U.S. Pat. No. 3,889,710 to Brost discloses a check valve in which a resilient disc prevents reverse flow by engaging an annular and concave Valve seat surface such that the area of the portion of the valve seat that engages the disc is proportionately much greater than that of the present invention. In the event the resilient disc were comprised of inert materials, the large valve seat surface of the disclosure would cause the diaphragm to stick to the valve seat particularly under conditions of high back pressure differentials. In addition, the disclosed invention provides a flow path by utilizing a disc of lesser outside diameter than the inside diameter of the flow chamber which allows the diaphragm to sift and become uneven in its operation.
In U.S. Pat. No. 4,141,379 to Manske, a check valve for use in medical applications is disclosed. The disclosed valve appears to be open in the presence of a low or no pressure differentials as the disc is attached to a transverse screen and $ is not in contact with the valve seat in the absence of back pressure differential. In addition, the disc of the disclosed valve is supported at its periphery and the valve is accordingly not opened by deformation of the disc but is apparently opened by the resilience of the screen or the axially movement of the o screen-disc assembly towards a series of stops at the outlet end. No stops are used at the inlet end of the disclosed valve as the valve seat diameter approximates the diameter of the inlet bore. Further the valve is adapted for push-on connections suitable only for very low pressure applications.
U.S. Pat. No. 4,354,492 to McPhee discloses a check valve adapted for push-on connections and designed for low pressure medical applications similar to the valve disclosed in Manske. The McPhee valve similarly has a valve seat of approximately the same diameter as the inlet bore and is closed by means of a disc which is not preloaded or biased against the valve seat thereby causing the valve to be normally in the open position in the absence of back pressure differential. The disclosed valve utilizes widely spaced disc stops radially spaced toward the perimeter of the disc such that the valve does not open by means of axial deformation of the perimeter of the disc.
U.S. Pat. No. 4,415,003 to Paradis, et al. discloses a valve using a flexible disc to control back flow without disc stops on the inlet end to prevent failure upon exposure to high back flow pressure differentials. The disclosed valve additionally has a wide flat annular valve seat surface such that a significantly greater area of the disc is exposed to back pressure than is exposed to the inlet pressure thereby requiring a relatively high pressure differential for opening.
U.S. Pat. No. 4,556,086 to Raines discloses a check valve similarly adapted for push-on connections appropriate for low pressure medical applications. The disclosed valve utilizes a dual substance disc biased against a valve seat by 2 supports spaced 180.degree. apart. Whereby the disclosed valve is opened by the bilateral U-shaped deformation of the dual disc system. No disc stops other than the valve seat are provided in the checked flow direction thereby making the disclosed valve subject to failure upon exposure to high back flow pressure differentials.
None of the foregoing references combine a valve seat of greater diameter than the inlet bore with central disc supports protecting against failure under high back pressure. Those valves that do provide a valve seat of significantly greater diameter than the inlet bore utilize a wide, flat valve seat surface which reduces the area of the disc that is exposed to the inlet pressure and thereby increases the pressure differential required to open the valve. In addition, currently available materials suitable for use in the disc when the check valve is used to control the flow of chemically aggressive or sensitive fluids, including elastomeric polytetrafluoroethylene (PTFE) substances, have a tendency to stick to the surfaces of the wide valve seats of the disclosed valves.
The referenced devices are generally not suitable for high flow, high pressure differential conditions due to the failure to provide both adequate disc support in both ends and sufficient flow capacity. Those of the referenced valves that appear to have relatively large flow capacity typically utilize posts to support the disc, if any support is used. Under high pressure differentials, the discs of such valves would be expected to tend to sag away from the posts and dislodge, blocking the flow passage or otherwise causing the valve to fail.